Plasma torch



United States Patent Int. Cl. Hin N88 US. 'Cl. 313146 6 Claims ABSTRACTOF THE DISCLOSURE In a plasma torch for spectrum analysis examinationprocesses a bar-shaped cathode and an annular anode are disposed in acasing which is subdivided by two discshaped apertured arc stabilizersinto three chambers. At least the two outer chambers are provided withtangential inlet apertures for a protective gas, while the centralchamber has a viewing aperture in front of which a spectrum analysisexamination device is arranged.

The disc-shaped arc stabilizers are disclosed to be made of graphite andto be mounted in discs having cavities through which a cooling mediumflows. The protective gas may, for example, be argon.

BACKGROUND OF THE INVENTION Field of the invention The present inventionrelates to a plasma torch for spectrum analysis examination processes.

Description of the prior art During recent years plasma torches forspectrum analysis examination have been disclosed in which the substanceto be analyzed is introduced into an electric arc. With an electric areconsiderably higher temperatures can be'obtained than with chemicalflames as previously used for such examination purposes. The use ofhigher temperatures, however, is advantageous because by thesetemperatures more energy is provided for dissociation and stimulation ofthe substances to be analyzed. As a result considerably more substancesas before may be examined by spectrum analysis processes.

A number of different types of plasma torches are already known to thoseskilled in the art. Of these torches those have proven to beparticularly suitable wherein the plasma of the electric arc isstabilized by diaphragms disposed between the arc cathode and anode.Said diaphragms, therefore, serve as are stabilizers.

By applying slight pressure above the atmospheric a plasma jet is forcedin perpendicular direction to the axis of the electric are through anaperture in the cham ber wall wherein the electric arc burns.Examination is then performed in this plasma jet. In the axis of the jettemperatures of up to 6,500" K. can be obtained. However, with theseprior art devices major difficulties are encountered in introducing thesubstances to be analyzed into the center of the jet.

SUMMARY OF THE INVENTION It is therefore an object of the presentinvention to provide a novel plasma torch which overcomes the abovementioned disadvantage. It is another object to provide a plasma torchwherein still higher temperatures can be obtained than with the knowndevices. It is a further object to provide a plasma torch which can beeasily dismounted and thus allows ready access to all its parts.

These objects are attained by arranging the cathode and the annularanode in a casing that is subdivided by two disc-shaped apertured arcstabilizers into three chambers, of which at least the two outerchambers are provided with tangential inlet apertures for a protectivegas. The central chamber has a viewing aperture in front of which aspectrum analysis examination device of known design is positioned.

The annular arc stabilizers consist of graphite rings mounted in brassor copper discs. The latter are provided with cavities through which acooling liquid passes.

The annular anode preferably consists of spectrally pure carbon and mayalso be disposed in a disc-shaped holder through which a cooling mediumflows. The cathode may consist of a throiated tungsten pencil which isfastened in a bar-shaped metal holder. The latter may be mounted axiallyslidably in an extensible spring housing.

Preferably at least part of the guide for the bar-shaped holder of thecathode consists of a hollow metallic disc through which also a coolingmedium flows and which at the same time serves to provide electricalconnection of the cathode to a cable connected to a DC. source.

In order to ensure easy dismantling of the torch and simpleinterchangeability of all parts the torch is constructed of disc-shapedand annular individual components which are held together by means oftwo clamp connectors.

DESCRIPTION OF THE DRAWINGS The objects and advantages of a plasma torchaccording to the invention will be more fully comprehended from thefollowing description when taken in conjunction with the appendingdrawings, wherein- FIG. 1 is a cross-sectional view of the plasma torchalong line II in FIG. 2, and

FIG. 2 is a plan view of the plasma torch.

Referring to the drawings, a plasma torch in accordance with theinevention comprises two discs 1 and 2, each of which has a central boreand which are made of electrically non-conductive, thermal insulatingmaterial. The two discs are held together by means of two clampconnectors 3 and 4. The clamp connectors 3 and 4 swivel around pin 3aand are hooked behind locking pins 3b. Four hollow discs 5, 6-, 7 and 8through which a cooling medium flows are positioned between the discs 1and 2. They are separated from one another by insulating rings 12, 13,14, made of a material capable of withstanding heat, for exampleasbestos cement. The discs 6, 7 and 8 are provided with central bores,in each of which carbon rings 9, 10 and 11 are respectively mounted. Thecarbon rings 9 and 10 serve as apertured stabilizers, while the carbonringe 11 serves as an anode and is connected electrically by means of acable 11a to a terminal 11b for the current supply.

In the interior of an extensible spring housing, a barshaped cathodeholder 17 is mounted in a cover 16 which closes the housing 15 and whichis made of electrically non-conductive material, said cathode holderbeing guided in a tube 18 of insulating material which is inserted inthe disc 1 and further guided by metal disc 5. The cathode holder 17extends through a central bore in the metal disc 5 and at its inner endcarries a thoriated tungsten pencil 19, which in addition is surroundedup to the height of its conical tip by a brass ring 20. The metal disc 5is connected by means of a cable 21 to the other pole 21b of the directcurrent supply. The brass ring 20 serves on the one hand to improve theelectrical connection of cathode pencil 19 to the disc 5 and on theother hand provides better transfer of heat.

The cavities containing coolant 35 in the discs 5, 6, 7 and 8 areconnected serially together through hose connections 22, 23, 24, 25, 26and 27 with a source of coolant, for example tap water. The electricalconductivity of water is so slight that it does not impair the arccurrent which may be between 30 and 60 amperes. It is advantageous forthe coolant to be allowed to flow first 3 through the cavity in thecathode disc 5 and thenthroug the other cavities, since the cathode issubjected to the greatest thermal load. The coolant is fed into the disc5 by the hose connection 25 and led out the opposite side by connection26. Connection 26 is now connected with hose connection 22. Water entersthe hollow area of disc 6 through connection 22 and leaves throughconnection 27. Connection 27 is now connected by a hose to 23 so thatthe coolant now flows into the hollow area of disc 7 from which it flowsout through another connection which is under hose connectin 27. Thislower hose connection is finally connected by a flexible hose withconnection 24 of the hollow area of disc 8. From disc 8 the water isfinally led off through a pipe connection underneath hose connection 27.This completes the circulation beginning with inlet connection 25,passing through four hollow areas to the outlet from the hollow areas ofdisc 8.

Beneath the annular anode 11 there is disposed, concentrically to itsbore, an atomiser 28 (shown in broken lines) for the introduction of theanalysis material into the plasma of the are burning between the cathode19 and anode 11. Bores having tangential inlet apertures 29 and 31 areprovided in the annular insulating discs 12 and 14 and are incommunication with gas admission connections 32 and 34 respectively.During operation a protective gas, for example argon, is injectedthrough these bores into the chambers containing the cathode or anode.The

tubular extension of the disc 7 is provided with cooling ribs andlikewise has a bore having a tangential inlet aperture, which is incommunication with a gas inlet connection 33. In the tubular extensionof the disc 7 there is in addition provided a viewing aperture 50through which it is possible to view the central chamber of the burner.The direction of viewing is indicated in FIG- URE 2.

The arc in the plasma torch is ignited by moving the cathode holderaxially in the direction of the anode against the pressure of the springof the extensible housing 15 until the brass ring 20 surrounding thecathode 19 makes contact with the annular anode 11. The spring then'brings the cathode 19 back into the operative position, while theelectric arc is formed between the cathode 19 and the anode 11.

It is advantageous to provide an adjustable apertu ed plate in thespectrophotometric viewing device, in order thereby to permit aselection of the v ewing point inside the plasma.

The above described plasma torch will permit observations in the plasmacore at temperatures of up to 17,000 K.

What is claimed is:

1. A plasma torch for spectrum analysis examination processes comprisingin combination a casing;

a bar-shaped cathode and an annular anode disposed in said casing alonga common axis;

a cathode holder;

an anode holder;

electrically conductive means adapted to connect said cathode to onepole of a D.C. source;

electrically conductive means adapted to connect said anode to the otherpole of said D.C. source;

two disc-shaped apertured arc stabilizers subdividing said casing intothree chambers;

a holder for each of said are stabilizers;

means adapted to cool said holders;

inlet apertures for a protective gas being provided in the outer two ofsaid chambers; and

a viewing aperture being provided in the central chamber in front ofwhich a spectrum analysis examination device can be disposed.

2. A plasma torch for spectrum analysis examination processes comprisingin combination and along a common aXlS a bar-shaped cathode and anannular anode;

an electrically conductive disc-shaped holder whereon said annular anodeis mounted, said disc being provided with cavities through which acooling medium flows;

electrically conductive means adapted to connect said anode holder toone pole of a D.C. source;

a bar-shaped holder whereto the cathode is fastened,

said holder being axially displaceable;

means adapted to guide said bar-shaped cathode holder,

said guide means comprising an electrically conductive disc providedwith cavities through which a cooling medium flows;

electrically conductive means adapted to connect said disc to the otherpole of a D.C. source;

two disc-shaped apertured arc stabilizers;

two metallic discs wherein said are stabilizers are secured, said discsbeing provided with cavities through which a cooling medium flows;

three insulating rings inserted between said discs and two insulatingapertured discs being positioned in front and to the rear of said discsand rings; clamping means adapted to press said discs and rings togetherso as to form a solid block, the latter constituting a casing which issubdivided by said are stabilizers into three chambers; an electricallynon-conductive hose connection adapted to connect serially said cavitiesin said discs; tangential inlet apertures for a protective gas beingprovided in the outer two of said chambers; and

a viewing aperture in the central chamber through which the substance tobe analyzed may be observed.

3. A plasma torch according to claim 2, wherein said protective gas isargon.

4. A plasma torch according to claim 2, wherein said apertured arcstabilizers comprise graphite rings.

5. A plasma torch according to claim 2, wherein said annular anodeconsists of spectrally pure carbon.

6. A plasma torch according to claim 2, wherein said cathode consists ofa thoriated tungsten pencil.

References Cited UNITED STATES PATENTS RAYMOND F. HOSSFELD, PrimaryExaminer US. Cl. X.R. 313 231 315-111

